OF MOVEMENT IN PLANTS 51 
irritation, can hardly be doubted in the light of observed facts” It remains to determine 
in what way these transmissions occur through the protoplasmic medium. At present, 
therefore, we must confine our considerations to continuity of protoplasm, in its structural 
relations to the tissues of the motile organs. 
In both the grape and the squash, the continuity appears most prominently in the 
collenchyma tissue of the rather thick hypodermis. It may also be observed without 
difficulty in the active parenchyma of all parts external to the xylem portions of the vascu- 
lar bundles. The same treatment, however, does not answer equally well for its detection 
in each case, owing to the different character of the tissues involved. In the pulvinus of 
Robinia, Gardiner” has already pointed out the clearly defined continuity which may be 
observed both in the parenchyma and in the bast. In the latter tissue we have found it 
to be most strikingly prominent, its exhibition being much less difficult than in the softer 
tissues, probably owing to the presence of numerous channels in the cell walls, which 
serve to localize and more sharply define the connecting filaments. 
The method employed for the exhibition of continuity must depend upon the charac- 
ter of the particular tissue involved. Any one of these methods, all of which have been 
employed by Gardiner and others, may be used according to circumstances. The first we 
may distinguish as the salt method. For the purpose there should be prepared a 10 p. c. 
solution of common salt. This has been recommended by Gardiner * as giving the best 
results in most cases, an opinion fully confirmed by our own experience. Perfectly fresh 
and thin sections are immersed in a suitable quantity of the solution and allowed to lie 
until wanted for the final staining. The action of the salt is to contract the protoplasm 
gradually into a compact, rounded mass, towards the centre of the cell, and thereby 
preserve intact the original connecting filaments, which then become drawn out into long, 
slender threads. There is, however, no appreciable change in the cell wall. A distinct 
development of continuity will generally be formed within a period of ten minutes, but, 
for good results, at least half an hour should be given; and since, with continued action, 
the salt consolidates all the contracted parts and thus renders all the filaments more 
distinct, an immersion of the sections for twenty-four or thirty-six hours may often prove 
desirable. If the solution be stronger than 10 p. c., the action is too rapid and many of 
the more delicate filaments snap during development, so that we then observe only their 
contracted remains upon the cell wall, with corresponding processes from the main 
protoplasmic mass. Treatment of this description answers admirably for all unmodified 
parenchyma tissue, such as that in the squash fruit, the flesh of the apple and pear, and in 
the pulvinus of the Robinia. It does not answer so well, however, in the case of thick- 
walled cells, whether collenchyma or bast. Then one of the following methods is to be 
preferred. 
The second method may be distinguished as the sulphuric acid process *. Very thin 
sections, freshly cut—one or two at a time, according to size—are placed upon the end of 
a glass slide or platinum foil. Surplus moisture is now removed in order to secure uni- 
form action of the acid. A drop of concentrated sulphuric acid is then placed on the slide 


1 Janczewski, Etudes Comparées sur la tubes Cribreux, 1881. Russow, Sitzberg. Dorpater Naturf. Ges., 1882, 
23, 257—327. Tangl, Pring’s Jahrb., xii. Strasburger, Bau und Wachsthum, 23. 
* Proc. Royal Soc., xxxv. 163—166. 3 [bid., xxiv. 272-—274. 
Bot. Centralb., xiv. 89—121. 
